DESCRIPTION(adapted from applicant's abstract): Since its discovery in the early 1970's, the middle temporal visual area (MT) of the primate has served as a valuable model of cortical sensory processing. Much is known about its basic receptive field properties. its connections, and its involvement in a number of important perceptual and behavioral functions. A rich body of literature exists describing interesting and important receptive field properties: selectivity for direction, speed. and binocular disparity and, very importantly, the existence of surrounds that are often selective for the same parameters and that render the neurons more selective for discontinuities in the visual world. The central goals of this application will be to understand the mechanisms underlying center-surround interactions in MT and the role that center-surround interactions play in perception and visually guided behavior. To study receptive field mechanisms, we will first examine in detail the space-time receptive field maps of MT neurons in alert monkeys. To learn more about the contributions of local circuitry to receptive field properties, we will study the intrinsic connections of MT with respect to functional maps of direction, binocular disparity, and center-surround interactions. We will also study the role of feedback connections in shaping the response properties of MT neurons by reversibly inactivating cortical regions that are reciprocally connected with MT. Finally, we will combine neuronal recordings, quantitative psychophysics, and microstimulation to study the role that neurons with center-surround receptive fields play in the spatial properties of motion perception. The overall product of the experiments detailed in this proposal will be a better understanding of the role that various sources of information play in shaping the response properties of neurons in MT and insights into the mechanisms by which MT receptive fields are constructed. We will also learn more about the hypothesized relationship between center-surround processing and the spatial properties of motion perception, including the important function of figure-ground segregation based on motion cues.